1. Technical Field
The invention concerns a storage control for implementing switching commands for access to storage cells for the writing and reading of data, which receives control commands allocated to the data, contains a command set for at least one storage type with command sequences of individual switch commands to be processed in a predetermined succession which are activated by control commands, which activates the switch commands of a command sequence corresponding to the current control command one after another, and activates the current switch command at a predetermined time after the previous switch command.
2. Discussion
A storage control of this kind may be used anywhere where for the purpose of electronic data processing data are stored in digital form in the storage cells of a memory. This is for example the case with computers. Increasingly, such storage controls are used with television apparatuses. The ever more complex control processes of electronic apparatuses are executed with the help of so-called micro controllers, which then also require a storage control. Examples here to be cited are control devices in the instrument panel of motor vehicles or even in more recent times developing navigation systems.
For write- or read- access to storage cells, control commands are allocated to the data which are to be written or read from these storage cells, which control commands for example contain information items about the storage address and whether there is to be a write or read situation. With the current memories, as for example SGRAM, SDRAM, MDRAM, PBSRAM etc., the control commands for writing and reading are sequences made up of individual commands. Technically conditioned, the switch commands corresponding to these control commands, respectively, are different for the individual storage types. A storage control is therefore generally associated with a special storage type and contains the specific command set for this type. Corresponding to the control commands, there is selected by the storage control for every command of a command sequence the corresponding switch command from the command set, and is activated. In this case the selection of the respective switch command depends on the respective control command and the previous switch command.
In order to execute the respective switch command a certain time scale is required. This certain time depends on the switch command itself and the storage type. With some storage types the certain time can also depend on the previous switch command. Partly, it is also possible in the so-called burst mode to gain access in parallel to the storage cells of some storage types. In order that these possibilities can be used meaningfully in respect of a more rapid processing speed, the storage control must accordingly implement these accessions in overlap.
Should one wish to use differing storage types with a data-/signal processing system, it is at present necessary to use the storage control associated with the respective storage type, in order to be able to use efficiently the respective, specific possibilities of this storage type. It should furthermore be born in mind that in the future other storage types with additional access possibilities may come on the market, which then also necessitate their own individual storage control.
In order to be able to apply a storage control more flexibly or in order not to be set with an existing switching on one storage type, it is desirable that several storage types can be controlled with one and the same storage control. A recently marketed storage control SH7708 from the firm Hitachi makes possible the use of DRAM, SDRAM, and PSRAM. It is certainly true that with this known storage control the specific advantages and options of the individual storage types are used insufficiently, for example, access to SDRAM memory is not effected in parallel in the so-called burst mode. This leads to losses in speed.
It is a task of the invention to indicate a storage control for the control of access to storage cells for the writing and reading of data, which can be quickly and simply changed over to the specific options of a certain storage type and which thereby uses efficiently the specific options of the respective storage type.
The task is solved by a storage control of the type mentioned at the beginning in that, dependent on the previous switch command and the current control command, the current switch command is activated, and that information items allocated to the storage cells can be supplied to the storage control which information items indicate the aforementioned predetermined time.
In this way, various predetermined times can be assigned to the respective switch command, dependent on which switch command was executed previously. Thus it can be achieved that for every switch command only the shortest necessary time has to be used. In this way altered performance characteristics of a type of memory may be taken into account simply by another command set and other predetermined times being used. In this way the storage control according to the invention can be used simply and flexibly.
In one development of the invention, a reference value is stored in a register for every switch command. The reference value here can correspond to the predetermined time and the register can be a write/read memory. In this way, with the use of different storage types, the predetermined time for each switch command can be altered particularly easily.
If a counter in the case of a further development counts the impulses of an impulse series since the activating of the switch command, the predetermined time for each switch command can be particularly easily measured.
In such a case it is of advantage if the counter reading is compared with the reference value, and if a signal is created, if the counter reading is the same as the reference value. A comparison of the counter reading with the reference value is achieved easily technologically and the signal can be used simply for activating the subsequent switch command. Preferably the signal is then registered and upon registering the signal the next switch command activated.
In a further development at least one switch command is already activated before the registration of the signal. In this way switch commands can be considered whose implementation demands only a relatively short time. In this case, no additional value for a predetermined time has to be stored anywhere.
In a further development of the invention the reference values for the switch commands are written in a set-up process into the register. Before the actual insertion of the storage facility in this way, by the writing of reference values into the register, the storage control can be rapidly and simply changed over to the specific options of a specific storage type.
In a further development of the invention the register also contains a value for the time after which the memory content should be refreshed. In the case of the dynamic memories typically used nowadays, a refreshing of the memory storage content is necessary after a certain time. By means of the above-described method, the elements described here up to now can also be used for preparation of the time for the refreshing process.
In a further development of the invention, a device is provided which creates a signal, if the current control command belongs to a new command sequence. This signal can be used advantageously for controlling the operation.
In a further development of the invention, operational control commands are created by the storage control for the running of individual switch commands of the command sequence in predetermined succession. This measure gives to the storage control in a simple manner the possibility of allocating the individual switch commands of a command sequence by means of the operational control commands.
In a further development of the invention activation commands are stored in a second register. The activation commands themselves are relatively independent of the storage type used and can therefore be used for various storage types. In order to adapt storage control to performance characteristics of another storage type, it is sufficient in such a case simply to execute the adaption of the predetermined time for the respective switch command, wherein the predetermined time can be stored in the first register.
Preferably, the switch commands are stored in a third register. In this fashion, the content of the register to be adapted can be overwritten.
With this further development, if the third register is a write/read memory or a programmable read-only-memory, in which switch commands are written in an initialization process, the storage control can be adapted through simple inscription of the switch commands into the third register before the insertion of the storage control to the specific performance characteristics of the storage type used.
A further development of the invention is distinguished by a signal being created if the current command sequence concerns the storage cells of the same line of the memory as the previous command sequence. If the storage cells of the storage type used can be used in the so-called burst mode, this signal can be utilized to control the storage cells accordingly.
The command set for the respective storage type can be determined by means of information items allocated to the storage cells. This is particularly advantageous when the storage control contains command sets for several different storage types. In this case the storage control then uses the command set suited to the respective storage type.
In a further development of the invention a signal is created when the writing or reading is over. This signal can be used with advantage to control the running.
Preferably, the signal can be returned with the address of origin for the access after its conclusion, e.g. it can be notified with the signal to the relevant processor that has caused the access, that the access has been concluded.
In such a case a signal can be created if the current switch command is the first switch command of a new command sequence. This signal can be used advantageously, for example, for measuring the time that has elapsed since the initiation of a command sequence.
If then the information items allocated to the storage cells also indicate the time after which after activating the first switch command of the respective new command sequence the writing or reading respectively is concluded, it is possible for the signal to be created at the time following the registering of the signal.